Method for forming dielectric film in trenches by PEALD using H-containing gas

ABSTRACT

A method for forming a dielectric film in a trench on a substrate by plasma-enhanced atomic layer deposition (PEALD) performs one or more process cycles, each process cycle including: (i) feeding a silicon-containing precursor in a pulse; (ii) supplying a hydrogen-containing reactant gas at a flow rate of more than about 30 sccm but less than about 800 sccm in the absence of nitrogen-containing gas; (iii) supplying a noble gas to the reaction space; and (iv) applying RF power in the presence of the reactant gas and the noble gas and in the absence of any precursor in the reaction space, to form a monolayer constituting a dielectric film on a substrate at a growth rate of less than one atomic layer thickness per cycle.

BACKGROUND

1. Field of the Invention

The present invention generally relates to a method for depositing adielectric film in a trench of a substrate by plasma-enhanced atomiclayer deposition (PEALD). The present invention also relates to a methodfor increasing a sidewall coverage of a dielectric film deposited byPEALD.

2. Related Art

As a method of depositing a film having a good step coverage, atomiclayer deposition (ALD) using chemisorption of a precursor is commonlyperformed. In this method, a film deposits more evenly in trenches ofsemiconductor circuits than does a film by CVD or the like. However, inplasma-enhanced atomic layer deposition (PEALD), since a sidewall of atrench of a substrate undergoes less ion bombardment than does a topsurface of the substrate, surface reaction at the sidewall is lessactive than on the top surface, causing a problem that an etch rate of afilm at the sidewall is different from (higher than) that on the topsurface. In particular, when a precursor has an adsorption inhibitionproblem due to e.g., the presence of hydrocarbon components in themolecule of the precursor, the step coverage of a film deposited on asidewall becomes low (e.g. 40% or less).

Conventionally, by increasing the process temperature or the like, thequality of a dielectric film (e.g., density, hardness) deposited on asidewall is improved so that the etch rate at the sidewall can bedecreased. However, the improvement is partial, and the problem indifferent etch rates between the sidewall and the top surface is notsufficiently resolved.

Any discussion of problems and solutions in relation to the related arthas been included in this disclosure solely for the purposes ofproviding a context for the present invention, and should not be takenas an admission that any or all of the discussion was known at the timethe invention was made.

SUMMARY

In some embodiments of the present invention, the thickness of filmdeposited on a target side of a trench of semiconductor circuits(substrate) can be controlled. In some embodiments, the thickness offilm deposited on a sidewall of a trench relatively increases, i.e., thethickness of film deposited on a top (blanket) surface of the substraterelatively decreases. In one approach, the thickness of film on asidewall of a trench can be controlled by controlling chemisorption of aprecursor on a surface using a chemisorption-inhibitor gas to which thesubstrate is exposed as a preliminary treatment before depositing a filmthereon, wherein functional groups exposed on the top surface of thesubstrate are terminated by Si—H bonds using a chemisorption-inhibitorgas such as hydrogen gas, thereby interfering with chemisorption of theprecursor on the top surface and relatively increasing the depositionrate of film on the sidewall. In some embodiments of the presentinvention, another approach other than the above approach is taken,wherein when depositing a silicon-based dielectric film such as a SiC orSiN film by PEALD, a hydrogen-containing gas is used as a reactant gasso as to cause not only deposition of a film but also etching of thefilm by a plasma. Since more species excited by a plasma reach a flatsurface, i.e., a top surface of a substrate and a bottom of a trench ofthe substrate, than excited species reaching a sidewall of thesubstrate, by controlling process parameters including feed quantity ofa precursor and intensity and duration of a hydrogen plasma, controllingand balancing deposition and etching of film can be accomplishedpredominantly on a flat surface, whereby the thickness of film at thesidewall of the trench can be adjusted relative to the thickness of filmon the flat surface of the substrate (the sidewall receives less effectof a plasma than does the flat surface). In the above, a film is beingdeposited by excited species of precursor while being etched by hydrogenand argon plasma, for example.

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomiclayer deposition) apparatus for depositing a dielectric film usable inan embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supplysystem using a flow-pass system (FPS) usable in an embodiment of thepresent invention.

FIG. 2 illustrates a PEALD process sequence according to an embodimentof the present invention.

FIG. 3 illustrates a PEALD process sequence according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid andmay be constituted by a single gas or a mixture of gases. Likewise, anarticle “a” or “an” refers to a species or a genus including multiplespecies. In this disclosure, a process gas introduced to a reactionchamber through a showerhead may be comprised of, consist essentiallyof, or consist of a precursor and a reactant gas. The reactant gas mayinclude a gas involving oxidizing and/or nitriding the precursor when RFpower is applied to the reactant gas. The reactant gas can be introducedcontinuously to a reaction space if it is not reactive to the precursorwithout RF power. The precursor can be introduced with a carrier gassuch as a noble gas. A gas other than the process gas, i.e., a gasintroduced without passing through the showerhead, may be used for,e.g., sealing the reaction space, which includes a seal gas such as anoble gas. In some embodiments, “film” refers to a layer continuouslyextending in a direction perpendicular to a thickness directionsubstantially without pinholes to cover an entire target or concernedsurface, or simply a layer covering a target or concerned surface. Insome embodiments, “layer” refers to a structure having a certainthickness formed on a surface or a synonym of film or a non-filmstructure. A film or layer may be constituted by a discrete single filmor layer having certain characteristics or multiple films or layers, anda boundary between adjacent films or layers may or may not be clear andmay be established based on physical, chemical, and/or any othercharacteristics, formation processes or sequence, and/or functions orpurposes of the adjacent films or layers. Further, in this disclosure,any two numbers of a variable can constitute a workable range of thevariable as the workable range can be determined based on routine work,and any ranges indicated may include or exclude the endpoints.Additionally, any values of variables indicated (regardless of whetherthey are indicated with “about” or not) may refer to precise values orapproximate values and include equivalents, and may refer to average,median, representative, majority, etc. in some embodiments. The terms“constituted by” and “having” refer independently to “typically orbroadly comprising”, “comprising”, “consisting essentially of”, or“consisting of” in some embodiments.

In the present disclosure where conditions and/or structures are notspecified, the skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation.

In all of the disclosed embodiments, any element used in an embodimentcan be replaced with any elements equivalent thereto, including thoseexplicitly, necessarily, or inherently disclosed herein, for theintended purposes. Further, the present invention can equally be appliedto apparatuses and methods.

In this disclosure, any defined meanings do not necessarily excludeordinary and customary meanings in some embodiments.

In some embodiments, the term “precursor” refers generally to a compoundthat participates in the chemical reaction that produces anothercompound, and particularly to a compound that constitutes a film matrixor a main skeleton of a film, whereas the term “reactant” refers to acompound that activates a precursor, modifies a precursor, or catalyzesa reaction of a precursor.

The dielectric film includes, but is not limited to, a low-k filmconstituted by a silicon carbide such as SiC, SiCN, and SiCON, a siliconoxide such as SiO, or a silicon nitride such as SiN, having a dielectricconstant of about 3 to 6, typically about 3.5 to 4.5 In someembodiments, the dielectric film is formed in trenches, vias, or otherrecesses including side walls and bottom surfaces (collectively referredto as “trenches”) by plasma-enhanced ALD or other plasma-assisted cyclicdeposition methods. The trench may have a depth of about 10 nm to about1,000 nm, typically about 100 nm to about 500 nm, and an aspect ratio ofabout 1 to about 10, typically about 2 to about 5 (e.g., a trench havinga width of about 30 nm, a depth of about 110 nm, and an aspect ratio ofabout 4, formed as a pattern in a silicon substrate). The thickness ofthe deposited dielectric film may be in a range of about 2 nm to about500 nm, typically about 10 nm to about 100 nm, more typically about 15nm to about 30 nm (a desired film thickness can be selected as deemedappropriate according to the application and purpose of film, etc.).

The embodiments will be explained with respect to preferred embodiments.However, the present invention is not limited to the preferredembodiments.

In an embodiment, in a method for forming a dielectric film in a trenchon a substrate by plasma-enhanced atomic layer deposition (PEALD)performing one or more process cycles, each process cycle comprises: (i)feeding a silicon-containing precursor in a pulse to a reaction spacewhere the substrate is placed, said precursor being constituted by oneor more hydrocarbon-containing compounds selected from the groupconsisting of: SiH₂R₂, Si₂H₂R₄, SiR₂X₂, Si₂R₆, SiH₃R, Si₂H₄R₂, SiH₂RX,C₃H₆SiH₂, C₂H₄SiH₂, C₂H₄Si₂H₂, SiNHSiR₄H₂, SiNHSiR₆, and SiHX₂R, whereineach X is independently chain or cyclic CxHy, and each R isindependently chain or cyclic C_(x)H_(y), cyclic N_(x)C_(y)H_(z),N(C_(x)H_(y))₂, N(C_(x)H_(y))H, O(C_(x)H_(y)), or OH, wherein x, y, andz are integers (e.g., x is an integer of 1 to 5, y is an integer of 1 to10, and z is an integer of 3 to 15); (ii) supplying ahydrogen-containing reactant gas to the reaction space at a flow rate ofmore than about 30 sccm but less than about 800 sccm (e.g., about 50sccm to about 500 sccm) in the absence of nitrogen-containing gas; (iii)supplying a noble gas to the reaction space; and (iv) applying RF powerto the reaction space in the presence of the hydrogen-containingreactant gas and the noble gas and in the absence of any precursor inthe reaction space, to form a monolayer constituting a dielectric filmon a substrate at a growth rate of less than one atomic layer thicknessper cycle. The growth rate per cycle or thickness of a monolayer refersto an average growth rate per cycle calculated based on the measuredthickness of a deposited film and the number of cycles performed for thedeposited film, or based on the total growth rate of the resultantdeposited dielectric film. The one atomic layer thickness refers to atheoretical thickness of one atomic layer formed from a precursor gaswithout considering lamination or the interface between monolayers. Theterm “monolayer” refers to a layer formed by one process cycle of PEALD,which may not be a continuous film.

In some embodiments, the growth rate of the monolayer is less than about0.1 nm per cycle (e.g., about 0.003 nm to about 0.09 nm). In general,the theoretical one atomic layer thickness is about 0.1 nm to about 0.5nm, typically about 0.2 nm to about 0.3 nm. When the above-mentionedhydrocarbon-containing compound is used as a precursor, due toadsorption inhibition of the precursor by the hydrocarbon components ona substrate surface, the average growth rate of the film per cycle on aflat horizontal surface (a blanket surface) becomes less than one atomiclayer thickness. In that case, in general, the growth rate of themonolayer on a sidewall is even worse than that on the blanket surface,resulting in a low step coverage on the sidewall (e.g., 40% or less).However, according to some embodiments of the present inventiondisclosed herein, the step coverage on the sidewall can surprisingly beincreased to 80% or higher.

In some embodiments, the precursor has a chemical formula where at leastone of X or R is an unsaturated hydrocarbon having, e.g., a carbondouble or triple bond. In general, when the precursor includes morecarbon atoms in its molecule, i.e., including fewer hydrogen atoms, moredeposition of film takes place, rather than etching of film. In someembodiments, the precursor has a cyclic structure. In some embodiments,the precursor is one or more compounds selected from the groupconsisting of: SiH₂R₂ such as dimethylsilane, divinylsilane, anddipyridylsilane; Si₂H₂R₄ such as tertamethyldisilane; SiR₂X₂ such asdivinyldimethylsilane and dimethyldipyridylsilane; Si₂R₆ such ashexamethydisilane; SiH₃R such as silylacetylene and allylsilane; Si₂H₄R₂such as divinyldisilane and dimethyldisilane; SiH₂RX such asviylmethylsilane; C₃H₆SiH₂ such as silacyclobutane; silacycloethane;disilacycloethane; SiNHSiR₄H₂ such as tetramethyldisilazane; SiNHSiR₆such as hexamethyldisilazane; and SiHX₂R such as dimethylpridyldisilane.

In some embodiments, the reactant gas is hydrogen gas. In someembodiments, the reactant gas is a hydrocarbon gas such as hexane Insome embodiments, the noble gas is argon. A combination of H₂ and Ar ismost effective in counteracting deposition of film, wherein H₂ in aplasma state likely causes chemical etching whereas Ar in a plasma statelikely causes physical spattering (bombardment at an angle of about 45°)on the surface of a substrate. Thus, H₂ in a plasma state is effectiveto etch predominantly a film on a flat surface, whereas Ar in a plasmastate is effective to etch rather uniformly a film on the flat surfaceand a film at the sidewall. Unlike Ar, He in a plasma state does notlikely cause physical spattering, and thus, a combination of H₂ and Ar,rather than a combination of H₂ and He, is used in some embodiments.

In some embodiments, a ratio of flow rate of the noble gas, typicallyAr, to flow rate of the hydrogen-containing reactant, typically hydrogengas, is about 5:1 to about 100:1, preferably about 10:1 to about 60:1.In the above, the flow rate of the noble gas includes a carrier gas forcarrying a precursor in addition to a dilution gas. When the flow rateof the hydrogen-containing reactant, typically hydrogen gas, is too low,etching effect is not sufficient to control growth rate of film on aflat surface, whereas when the flow rate is too high, etching effect ispredominant and no film is deposited on the flat surface.

When a hydrogen plasma is used, both the etching effect and thedeposition effect can be obtained, and can be balanced by adjusting theflow rate of hydrogen, the number of RF pulses per cycle, the feed of aprecursor, etc. The etching by a hydrogen plasma may occur as follows,for example:SiO₂+4H—Si+2H₂O,SiO₂+2H→Si+H₂O₂Si+xH→SiH_(x)

On the other hand, deposition by a hydrogen plasma may occur viaremoving a ligand which promotes chemisorption, and via formation ofdangling bonds. Further, deposition may occur through re-deposition ofdissociated components by etching.

In some embodiments, in step (iii), the noble gas is supplied to thereaction space at a flow rate of about 1,000 sccm to about 5,000 sccm,preferably about 2,000 sccm to about 4,000 sccm.

In some embodiments, the reactant gas is supplied continuously to thereaction space throughout each process cycle. In some embodiments, thenoble gas is continuously supplied to the reaction space throughout theprocess cycle.

In some embodiments, in step (iv), no gas other than the reactant gasand the noble gas is supplied to the reaction space.

In some embodiments, in step (i), the precursor is fed in an amount ofabout 0.00002 g/cycle to about 0.01 g/cycle and in a pulse having aduration of about 0.1 seconds to about 1.0 seconds. Since ALD is aself-limiting adsorption reaction process, the number of depositedprecursor molecules is determined by the number of reactive surfacesites and is independent of the precursor exposure after saturation, anda supply of the precursor is such that the reactive surface sites aresaturated thereby per cycle. In other embodiments the plasma may begenerated remotely and provided to the reaction chamber. The feed amountof precursor can be determined depending on the molecular weight ofprecursor.

In some embodiments, each process cycle further comprises a purging stepbetween steps (i) and (iv), and between steps (iv) and (i) if theprocess cycle is repeated. In some embodiments, in step (iv), RF poweris applied to the reaction space in two occurrences between which apurging step is conducted (in some embodiments, three or moreoccurrences per cycle). In some embodiments, in step (iv), RF powerapplied to the reaction space is about 0.028 W/cm² to about 0.28 W/cm²,preferably 0.07 W/cm² to about 0.21 W/cm². When a combination of H₂ andAr is used as a reactant gas, etching can occur at a low RF power. Insome embodiments, the duration of a pulse of RF power is about 0.2seconds to about 5 seconds, preferably about 0.5 seconds to about 1second. The longer the duration of a pulse of RF power, the greater thereduction of thickness becomes. If application of RF power is dividedinto multiple sessions, the reduction of thickness can significantly belowered. By adjusting the duration of RF power application and thenumber of RF power applications per cycle, the step coverage at thesidewall and on the flat surface can be desirably adjusted.

In some embodiments, the temperature during the process cycle is about50° C. to about 500° C., preferably about 100° C. to about 300° C.

In some embodiments, the dielectric film is a film of SiC, SiCN, SiN,SiOCN, or SiO. For example, a SiN film can be deposited when a precursorhaving a Si—N bond such as silylamine compounds or aminosilane compoundsis used, whereas a SiO film can be deposited when a precursor having aSi—O bond such as alkoxide compounds is used, even when only hydrogengas and argon gas are used as a reactant gas.

In some embodiments, a sidewall coverage of the deposited dielectricfilm is about 80% or higher, typically about 80% to about 130%, whereinthe sidewall coverage is defined as a ratio of thickness of film on asidewall of the trench to thickness of film on a blanket surface of thetrench.

In some embodiments, a method for increasing a sidewall coverage of adielectric film deposited according to any deposition method disclosedherein is provided, wherein in step (i), the precursor is fed in a pulsehaving a first duration, in step (ii), the reactant gas is supplied at afirst flow rate, and in step (iv), RF power is applied in a pulse havinga first duration, and the dielectric film has a first sidewall coverage,said sidewall coverage being defined as a ratio of thickness of film ona sidewall of the trench to thickness of film on a blanket surface ofthe substrate, said method comprising: (a) setting a second duration ofthe pulse of the precursor in step (i), a second flow rate of thereactant gas in step (ii), and a second duration of the pulse of RFpower in step (iv), wherein at least one of the second flow rate of thereactant gas and the second duration of the pulse of RF power is higherthan the first flow rate of the reactant gas and the first duration ofthe pulse of RF power, respectively, and/or the second duration of thepulse of the precursor is shorter than the first duration of the pulseof the precursor; and (b) repeating steps (i) to (iv) using the secondflow rate of the reactant gas and the second duration of the pulse of RFpower, thereby depositing a dielectric film having a second sidewallcoverage which is higher than the first sidewall coverage.

In some embodiments, the film is deposited by PEALD under conditionsshown in Table 1 below.

TABLE 1 (the numbers are approximate) Conditions for Deposition CycleSubstrate temperature 50 to 500° C. (preferably 100 to 400° C.) Pressure100 to 1000 Pa (preferably 200 to 500 Pa) Precursor pulse 0.1 to 3 Sec(preferably 0.1 to 1 Sec) Precursor purge 0.3 to 10 Sec Flow rate ofreactant 50 to 1000 sccm (preferably 100 to (continuous) 300 sccm)Carrier gas e.g., argon Dilution gas e.g., argon Flow rate of carrier/1000 to 5000 sccm (preferably dilution gas (continuous) 2000 to 4000sccm) RF power (13.56 MHz) 50 to 200 W (preferably 50 to 150 W) for a300-mm wafer RF power pulse (total) 0.2 to 5 sec (preferably 0.5 to 1sec) Purge 0.1 to 2 Sec Growth rate per cycle 0.005 to 0.08 nm/cycleTotal thickness [nm] 3 to 20 Nm

FIG. 2 illustrates a PEALD process sequence according to an embodimentof the present invention. In this disclosure, the width of each columndoes not necessarily represent the actual time length, and a raisedlevel of the line in each row represents an ON-state whereas a bottomlevel of the line in each row represents an OFF-state. The depositioncycle includes steps of feeding a precursor to a reaction zone, purgingthe reaction zone, applying RF power to the reaction zone, and purgingthe reaction zone in this order, wherein a purge/carrier gas is suppliedcontinuously to the reaction zone throughout the entire steps of thedeposition cycle, and a reactant gas for deposition is suppliedcontinuously to the reaction zone throughout the entire steps of thedeposition cycle. In the deposition cycle, steps of feeding theprecursor, purging the reaction zone, applying RF power to the reactionzone, and purging the reaction zone can be repeated p times (p is aninteger of 5 to 100, typically 8 to 50), depending on the targetcompositions and quality of the film, although repeating is notrequired.

In this disclosure, the word “continuously” refers to at least one ofthe following: without breaking a vacuum, without being exposed to air,without opening a chamber, as an in-situ process, without interruptionas a step in sequence, and without changing main process conditions,depending on the embodiment. In some embodiments, an auxiliary step suchas a delay between steps or other step immaterial or insubstantial inthe context does not count as a step, and thus, the word “continuously”does not exclude an intervening auxiliary step.

FIG. 3 illustrates a PEALD process sequence according to anotherembodiment of the present invention. In this sequence, after thesequence illustrated in FIG. 2, the deposition cycle further includessteps of applying again RF power (“RF-2”) to the reaction zone, andpurging the reaction zone in this order. In other words, application ofRF power illustrated in FIG. 2 is divided into two sessions, i.e., theapplication of RF power comprises a first application of RF power,purging, and a second application of RF power. In some embodiments, theapplication of RF power may comprise more than two applications of RFpower (e.g., three or four sessions). The first application and thesubsequent application of RF power can be conducted in the same manneror in different manners, e.g., at different pulse durations (the firstduration is shorter or longer than the second duration), differentintensities (the first intensity is lower or higher than the secondintensity), etc.

In the sequence illustrated in FIG. 2, the precursor is supplied in apulse using a carrier gas which is continuously supplied. This can beaccomplished using a flow-pass system (FPS) wherein a carrier gas lineis provided with a detour line having a precursor reservoir (bottle),and the main line and the detour line are switched, wherein when only acarrier gas is intended to be fed to a reaction chamber, the detour lineis closed, whereas when both the carrier gas and a precursor gas areintended to be fed to the reaction chamber, the main line is closed andthe carrier gas flows through the detour line and flows out from thebottle together with the precursor gas. In this way, the carrier gas cancontinuously flow into the reaction chamber, and can carry the precursorgas in pulses by switching the main line and the detour line. FIG. 1Billustrates a precursor supply system using a flow-pass system (FPS)according to an embodiment of the present invention (black valvesindicate that the valves are closed). As shown in (a) in FIG. 1B, whenfeeding a precursor to a reaction chamber (not shown), first, a carriergas such as Ar (or He) flows through a gas line with valves b and c, andthen enters a bottle (reservoir) 20. The carrier gas flows out from thebottle 20 while carrying a precursor gas in an amount corresponding to avapor pressure inside the bottle 20, and flows through a gas line withvalves f and e, and is then fed to the reaction chamber together withthe precursor. In the above, valves a and d are closed. When feedingonly the carrier gas (noble gas) to the reaction chamber, as shown in(b) in FIG. 1B, the carrier gas flows through the gas line with thevalve a while bypassing the bottle 20. In the above, valves b, c, e, andf are closed.

The precursor may be provided with the aid of a carrier gas. Since ALDis a self-limiting adsorption reaction process, the number of depositedprecursor molecules is determined by the number of reactive surfacesites and is independent of the precursor exposure after saturation, anda supply of the precursor is such that the reactive surface sites aresaturated thereby per cycle. A plasma for deposition may be generated insitu, for example, in an ammonia gas that flows continuously throughoutthe deposition cycle. In other embodiments the plasma may be generatedremotely and provided to the reaction chamber.

As mentioned above, each pulse or phase of each deposition cycle ispreferably self-limiting. An excess of reactants is supplied in eachphase to saturate the susceptible structure surfaces. Surface saturationensures reactant occupation of all available reactive sites (subject,for example, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage. In some embodiments the pulse time ofone or more of the reactants can be reduced such that completesaturation is not achieved and less than a monolayer is adsorbed on thesubstrate surface.

The process cycle can be performed using any suitable apparatusincluding an apparatus illustrated in FIG. 1A, for example. FIG. 1A is aschematic view of a PEALD apparatus, desirably in conjunction withcontrols programmed to conduct the sequences described herein, usable insome embodiments of the present invention. In this figure, by providinga pair of electrically conductive flat-plate electrodes 4, 2 in paralleland facing each other in the interior 11 (reaction zone) of a reactionchamber 3, applying HRF power (13.56 MHz or 27 MHz) 20 to one side, andelectrically grounding the other side 12, a plasma is excited betweenthe electrodes. A temperature regulator is provided in a lower stage 2(the lower electrode), and a temperature of a placed thereon is keptconstant at a given temperature. The upper electrode 4 serves as ashower plate as well, and reactant gas (and noble gas) and precursor gasare introduced into the reaction chamber 3 through a gas line 21 and agas line 22, respectively, and through the shower plate 4. Additionally,in the reaction chamber 3, a circular duct 13 with an exhaust line 7 isprovided, through which gas in the interior 11 of the reaction chamber 3is exhausted. Additionally, a transfer chamber 5 disposed below thereaction chamber 3 is provided with a seal gas line 24 to introduce sealgas into the interior 11 of the reaction chamber 3 via the interior 16(transfer zone) of the transfer chamber 5 wherein a separation plate 14for separating the reaction zone and the transfer zone is provided (agate valve through which a wafer is transferred into or from thetransfer chamber 5 is omitted from this figure). The transfer chamber isalso provided with an exhaust line 6. In some embodiments, thedeposition of multi-element film and surface treatment are performed inthe same reaction space, so that all the steps can continuously beconducted without exposing the substrate to air or otheroxygen-containing atmosphere. In some embodiments, a remote plasma unitcan be used for exciting a gas.

In some embodiments, in the apparatus depicted in FIG. 1A, the system ofswitching flow of an inactive gas and flow of a precursor gasillustrated in FIG. 1B (described earlier) can be used to introduce theprecursor gas in pulses without substantially fluctuating pressure ofthe reaction chamber.

In some embodiments, a dual chamber reactor (two sections orcompartments for processing wafers disposed closely to each other) canbe used, wherein a reactant gas and a noble gas can be supplied througha shared line whereas a precursor gas is supplied through unsharedlines.

A skilled artisan will appreciate that the apparatus includes one ormore controller(s) (not shown) programmed or otherwise configured tocause the deposition and reactor cleaning processes described elsewhereherein to be conducted. The controller(s) are communicated with thevarious power sources, heating systems, pumps, robotics, and gas flowcontrollers or valves of the reactor, as will be appreciated by theskilled artisan.

The present invention is further explained with reference to workingexamples below. However, the examples are not intended to limit thepresent invention. In the examples where conditions and/or structuresare not specified, the skilled artisan in the art can readily providesuch conditions and/or structures, in view of the present disclosure, asa matter of routine experimentation. Also, the numbers applied in thespecific examples can be modified by a range of at least ±50% in someembodiments, and the numbers are approximate.

EXAMPLES

A silicon carbide film was formed on a Si substrate (0300 mm) havingtrenches with an aspect ratio of 3.5 (a width of 30 nm, and a depth of110 nm) by PEALD using a sequence illustrated in FIG. 2 or 3, one cycleof which was conducted under the common conditions shown in Table 2(process cycle) below using the PEALD apparatus illustrated in FIG. 1Aand a gas supply system (FPS) illustrated in FIG. 2 with the specificconditions and sequence indicated in Table 3.

TABLE 2 (the numbers are approximate) Common Conditions for ProcessCycle Substrate temperature 300.° C. Pressure 300 Pa Carrier gas anddilution gas Ar Reactant gas H₂ Flow rate of carrier/dilution gas 2000sccm/1000 sccm (continuous) (3000 sccm total) Purge after precursor feedpulse 1 sec Purge after RF power pulse 1 sec RF power 100 W TargetThickness (nm) 10.

TABLE 3 (the numbers are approximate) Feed RF H₂ Feed amount pulse flowSequence (seconds) (g/cycle) (seconds) Precursor (sccm) *1 FIG. 2 1 0.041 DVDMS 0 *2 FIG. 2 0.1 0.004 1 DVDMS 800 *3 FIG. 2 1.0 0.002 1 HMDS 0 4 FIG. 2 1 0.002 1 HMDS 50  5 FIG. 2 0.8 0.0016 1 HMDS 50  6 FIG. 2 0.60.0012 1 HMDS 50  7 FIG. 2 0.5 0.001 1 HMDS 50  8 FIG. 2 0.1 0.0002 1HMDS 50  9 FIG. 2 0.5 0.001 0.5 HMDS 50 10 FIG. 2 0.1 0.0002 0.5 eachHMDS 50 11 FIG. 2 0.1 0.004 0.5 each DVDMS 50 12 FIG. 2 0.1 0.004 1DVDMS 50 13 FIG. 2 0.1 0.004 1 DVDMS 300

In Table 3, the Example numbers with “*” indicate comparative examples.Each obtained film was evaluated. Table 4 shows the results ofevaluation. DVDMS is divinyldimethylsilane, and HMDS ishexamethyldisilane.

TABLE 4 (the numbers are approximate) GPC Sidewall Coverage (nm/cycle)@AR3 (%) Remarks *1 0.03   35% No damage *2 — — Great damage *3 0.12  40% No damage 4 0.07   80% No damage 5 0.05   85% No damage 6 0.02  94% No damage 7 0.009 125% No damage 8 0.006 130% Slight damage 9 0.007130% No damage 10 0.004 150% No damage 11 0.06   85% No damage 12 0.02 115% No damage 13 0.01  130% No damage

In Table 4, “GPC” represents growth rate per cycle, “SidewallCoverage@AR3” represents a percentage of thickness of film deposited ona sidewall relative to thickness of film deposited on a blanket surfaceat a trench having an aspect ratio of 3, and “Remarks” describes damageobserved on a surface of an underlying layer after deposition.

In the above examples, when no hydrogen gas was used as a reactant inExample 1, the sidewall coverage was significantly low, since nohydrogen gas was used, and sufficient argon plasma did not reach thesidewall of the trench, whereby sufficient active sites on thesilicon-containing hydrocarbon precursor were not formed at thesidewall, i.e., the sidewall coverage was poor (35%). On the other hand,when excessive hydrogen gas (800 sccm) was used in Example 2, etchingtook place particularly on the top surface, and no film was deposited.However, when an appropriate quantity of hydrogen gas was used inExamples 12 (50 sccm) and 13 (300 sccm), etching desirably took place onthe top surface, thereby interfering with deposition of film on the topsurface and significantly increasing the sidewall coverage (115% inExample 12; 130% in Example 13). Further, when RF power was applied intwo sessions in Example 11, the etching effect by hydrogen gas becameweaker, and deposition by hydrogen gas was promoted. As a result, theGPC was increased, especially at the sidewall, thereby increasing thesidewall coverage (85%) as well as the GPC (0.06 nm/cycle), as comparedwith Example 12 (the sidewall coverage was 115%, and the GPC was 0.02nm/cycle) and Example 1 (the sidewall coverage was 35%, and the GPC was0.03 nm/cycle). The above differences between Examples 11 and 12 areopposite to those between Examples 8 and 10 discussed below. This may bebecause in Examples 11 and 12, the precursor possessed a carbon doublebond (vinyl), and when the double bond was opened by a hydrogen plasma,chemisorption and formation of dangling bonds could have been promoted,more than etching.

When the duration of feed pulse was increased from 0.1 second (Example8) to 0.5 seconds (Example 7), 0.6 seconds (Example 6), 0.8 seconds(Example 5), and 1.0 seconds (Example 4), the GPC was increasedaccordingly from 0.006 nm/cycle (Example 8) to 0.009 nm/cycle (Example7), 0.02 nm/cycle (Example 6), 0.05 nm/cycle (Example 5), and 0.07nm/cycle (Example 4), whereas the sidewall coverage was decreasedaccordingly from 130% (Example 8) to 125% (Example 7), 94% (Example 6),85% (Example 5), and 80% (Example 4). When comparing Example 4 (with 50sccm of hydrogen gas) and Example 3 (with 0 sccm of hydrogen gas), theGPC was lower in Example 4 (0.07 nm/cycle) than that in Example 3 (0.12nm/cycle), the sidewall coverage was significantly higher in Example 4(80%) than that in Example 3 (40%) due to the etching effect of ahydrogen plasma which was more prominent on the blanket surface than thesidewall. When the duration of feed pulse was as short as 0.1 second inExample 8, fine damage on the surface of the substrate was observed.Further, when the duration of RF power pulse was shorter in Example 9(0.5 seconds) than in Example 8 (1.0 second), the GPC was slightlyincreased whereas the sidewall coverage was substantially unchanged.Further, when RF power was applied in two sessions in Example 10 ascompared with Example 8 (one session), the etching effect by hydrogengas became stronger, and deposition by hydrogen gas was least promoted.As a result, the GPC was low (0.004 nm/cycle), as compared with Example8 (0.006 nm/cycle). The above differences between Examples 8 and 10 areopposite to those between Examples 11 and 12 discussed above. This maybe because in Examples 8 and 10, the precursor did not possess a carbondouble bond, and the etching effect of a hydrogen plasma became moreprominent by two-session application, resulting in lower GPC in Example10 (0.004 nm/cycle) than that in Example 8 (0.006 nm/cycle), and highersidewall coverage in Example 10 (150%) than that in Example 8 (130%).

Accordingly, it was confirmed that by adjusting the duration of feedpulse, the duration of RF power pulse, and/or the flow rate of hydrogengas, the sidewall coverage and the GPC can be desirably adjusted.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

We claim:
 1. A method for forming a dielectric film in a trench on asubstrate by plasma-enhanced atomic layer deposition (PEALD) performingone or more process cycles, each process cycle comprising: (i) feeding asilicon-containing precursor in a pulse to a reaction space where thesubstrate is placed, said silicon-containing precursor being constitutedby one or more hydrocarbon-containing compounds selected from the groupconsisting of: SiH₂R₂, Si₂H₂R₄, SiR₂X₂, Si₂R₆, SiH₃R, Si₂H₄R₂, SiH₂RX,C₃H₆SiH₂, C₂H₄SiH₂, C₂H₄Si₂H₂, SiNHSiR₄H₂, SiNHSiR₆, and SiHX₂R, whereineach X is independently chain or cyclic CxHy, and each R isindependently chain or cyclic C_(x)H_(y), cyclic N_(x)C_(y)H_(z),N(C_(x)H_(y))₂, N(C_(x)H_(y))H, O(C_(x)H_(y)), or OH, wherein x, y, andz are integers; (ii) supplying a hydrogen-containing reactant gas to thereaction space at a flow rate of more than about 30 sccm but less thanabout 800 sccm in the absence of nitrogen-containing gas; (iii)supplying a noble gas to the reaction space; and (iv) applying RF powerto the reaction space in the presence of the hydrogen-containingreactant gas and the noble gas and in the absence of any precursor inthe reaction space, to form a monolayer constituting a dielectric filmon a substrate at a growth rate of less than one atomic layer thicknessper cycle.
 2. The method according to claim 1, wherein the growth rateof the monolayer is less than 0.1 nm/cycle.
 3. The method according toclaim 1, wherein the precursor has a chemical formula where at least oneof X or R is an unsaturated hydrocarbon.
 4. The method according toclaim 1, wherein the precursor has a cyclic structure.
 5. The methodaccording to claim 1, wherein the silicon-containing precursor is one ormore compounds selected from the group consisting of: dimethylsilane,divinylsilane, dipyridylsilane, tertamethyldisilane,divinyldimethylsilane, dimethyldipyridylsilane, hexamethydisilane,silylacetylene, allylsilane, divinyldisilane, dimethyldisilane,viylmethylsilane, silacyclobutane, silacycloethane, di silacycloethane,tetramethyldisilazane, hexamethyldisilazane, and dimethylpridyldisilane.6. The method according to claim 1, wherein the reactant gas is hydrogengas.
 7. The method according to claim 1, wherein the noble gas is argon.8. The method according to claim 1, wherein the reactant gas is suppliedcontinuously to the reaction space throughout each process cycle.
 9. Themethod according to claim 1, wherein the noble gas is continuouslysupplied to the reaction space throughout the process cycle.
 10. Themethod according to claim 1, wherein a ratio of flow rate of the noblegas to flow rate of the reactant is about 10:1 to about 60:1.
 11. Themethod according to claim 1, wherein in step (iii), the noble gas issupplied to the reaction space at a flow rate of about 1,000 sccm toabout 5,000 sccm.
 12. The method according to claim 1, wherein in step(iv), no gas other than the reactant gas and the noble gas is suppliedto the reaction space.
 13. The method according to claim 1, wherein instep (i), the silicon-containing precursor is fed in an amount of about0.00002 g/cycle to about 0.01 g/cycle and in a pulse having a durationof about 0.1 seconds to about 1.0 second.
 14. The method according toclaim 1, wherein each process cycle further comprises a purging stepbetween steps (i) and (iv), and between steps (iv) and (i) when theprocess cycle is repeated.
 15. The method according to claim 1, whereinin step (iv), RF power is applied to the reaction space in twooccurrences between which a purging step is conducted.
 16. The methodaccording to claim 1, wherein in step (iv), RF power applied to thereaction space is about 0.028 W/cm² to about 0.28 W/cm².
 17. The methodaccording to claim 1, wherein the temperature during the process cycleis about 50° C. to about 500° C.
 18. The method according to claim 1,wherein the dielectric film is a film of SiC, SiCN, SiN, SiOCN, or SiO.19. The method according to claim 1, wherein a sidewall coverage of thedeposited dielectric film is about 80% or higher, wherein the sidewallcoverage is defined as a ratio of thickness of film on a sidewall of thetrench to thickness of film on a blanket surface of the trench.
 20. Amethod for increasing a sidewall coverage of a dielectric film depositedaccording to claim 1 wherein in step (i), the precursor is fed in apulse having a first duration, in step (ii), the reactant gas issupplied at a first flow rate, and in step (iv), RF power is applied ina pulse having a first duration, and the dielectric film has a firstsidewall coverage, said sidewall coverage being defined as a ratio ofthickness of film on a sidewall of the trench to thickness of film on ablanket surface of the trench, said method comprising: (a) setting asecond duration of the pulse of the precursor in step (i), a second flowrate of the reactant gas in step (ii), and a second duration of thepulse of RF power in step (iv), wherein at least one of the second flowrate of the reactant gas and the second duration of the pulse of RFpower is higher than the first flow rate of the reactant gas and thefirst duration of the pulse of RF power, respectively, and/or the secondduration of the pulse of the precursor is shorter than the firstduration of the pulse of the precursor; and (b) repeating steps (i) to(iv) using the second flow rate of the reactant gas and the secondduration of the pulse of RF power, thereby depositing a dielectric filmhaving a second sidewall coverage which is higher than the firstsidewall coverage.